Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world, so the safety profile is covered. The description adds two useful behavioral facts: input is case-insensitive English, and cost is plan-dependent and not in the public credit manifest — the latter is genuinely valuable for an agent.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Very short and front-loaded: the core purpose is in the first clause, followed by compact group/cost metadata. No wasted prose, though the bracketed cost line is boilerplate shared across the family.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values needn't be explained, and annotations carry the safety profile, so the description is adequate on those fronts. What is missing is routing information among the numerous crystal siblings, which matters given the crowded toolset.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so sign, fields and precision are already documented. The description's note that the sign is a case-insensitive English name adds only marginal clarification (and slightly softens the schema's 'lowercase English name' wording). Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific resource (crystals) and filter (zodiac sign), which distinguishes it from siblings like crystals_by_chakra and crystals_by_purpose. However, it never names those alternatives, so the agent must infer the distinction from the tool name alone.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no explicit when-to-use guidance, no prerequisites, and no mention of the sibling crystal-lookup tools (astroway_esoteric_crystals, by_chakra, by_purpose, recommend) that an agent would need to choose between. Usage is only implied by the phrase 'indexed for a given zodiac sign'.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.